Lithiation of electrodes for energy storage devices and method of making same

ABSTRACT

A method for lithiation of an electrode includes providing an electrode to be lithiated, providing a piece of lithium metal with predetermined weight attached to a conductive material, attaching the conductive material to a current collector of the electrode to be lithiated or to a metal tab connected to or from the electrode to be lithiated, placing the electrode to be lithiated, the piece of lithium, and the conductive material in a container, and filling the container with an electrolyte containing a lithium salt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims the benefit of U.S. ProvisionalPatent Application Ser. No. 62/925,682 filed Oct. 24, 2019 and entitled“LITHIATION OF ELECTRODES FOR ENERGY STORAGE DEVICES AND METHOD OFMAKING SAME,” the entire disclosure of which is hereby incorporated byreference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND 1. Technical Field

Apparatuses and methods consistent with the present inventive conceptrelate to energy storage devices, and more particularly to electrodesfor energy storage devices.

2. Description of the Related Art

Lithium (Li) pre-doped electrodes, or lithiated electrodes, are widelyused in energy storage devices, for example, lithium-ion (Li-ion)batteries and Li-ion capacitors.

In the external Li attachment and pre-dope method, an electrode pack isconstructed with at least one positive electrode, at least oneseparator, at least one Li film laminated on a current collector, and atleast one negative electrode. The negative electrode is connected to theLi film through welding of the current collector tabs. The electrodepack is immersed in electrolyte that contains Li ions. Through thepre-dope process, the Li film is converted into Li ions and the Li ionsmigrate and are doped into the negative electrode.

In the external Li attachment and pre-dope method, thin Li metal filmsare normally provided on the uppermost and lowermost layers of anelectrode package. During the Li pre-dope process, the Li ions have totravel through the electrode and separator layers. One of therequirements is that the current collectors inside the electrodes needsto be in a mesh or perforation format, which is costly, and the Li maybe non-uniformly doped into the stacked negative electrode layers eventhough the current collectors in the center of the electrodes are madeporous. Long manufacture time is reported to uniformly dope lithium tothe negative electrode inside the electrode laminates. Further, as Limetal is very sensitive to moisture, the entire operation of themanufacture of the electrodes attached to Li metal, the electrode packs,and the energy storage devices must be carried out in a full scale dryroom, which requires high capital investment and high energyconsumption. Therefore, the long manufacture cycle time plus the dryroom operation requirements, makes this high cost method lesscompetitive in the energy storage device industry.

In order to improve the long manufacture time and high cost necessaryfor the external Li attachment and pre-dope method, direct contactmethods were proposed by different inventors as described, for example,in U.S. Patent Application Pub. No. 2017/0062815, the entire contents ofwhich is incorporated by reference herein. In the direct contactmethods, Li powder or Li film with patterns were pressed directly ontothe electrode surface layer. The direct contact methods largelyshortened the Li pre-dope time. However, Li metal powder or foils mayremain on the electrode surface after completion of the pre-dopingprocess, which again presents a high safety issue for the energy storagedevices. More detrimentally, instantaneous electrical shorting betweenthe Li metal and the negative electrode active layer materials (i.e.,the surface of the electrode) induced by immersing the electrode packinto electrolyte caused severe reactions. These severe reactionsresulted in damage to the electrode and separator, resulting in sub-parbatteries and capacitors. Further, the direct contact method stillrequires the whole manufacture process being carried out in a full-scaledry room environment, which again, requires high capital investment andhigh energy consumption in operations.

In order to reduce the energy storage device manufacture time and cost,to eliminate the need for expensive full scale dry room operations, andto prevent the damage caused to the electrode by direct contact, newlithiation methods to produce Li pre-doped electrodes for energy storagedevices have been newly developed as set forth herein.

BRIEF SUMMARY

Various embodiments provide lithiated or pre-doped electrodes andmethods for fabricating lithiated or pre-doped electrodes. Lithiationcan be introduced to the electrode at the different assembly stages ofan energy storage device.

Steps and corresponding stages of a typical large scale energy storagedevice assembly process are listed below:

1. Prepare an electrode in a roll to roll format (Stage 1)

2. Prepare an electrode pack, e.g., wound or stacked electrode(s) andseparator(s) (Stage 2)

3. Insert the electrode pack into a case (e.g. a cylindrical orprismatic container or a pouch), the cell assembly (Stage 3)

4. Vacuum dry the cell assembly

5. Impregnation of the electrolyte

6. Seal the case

According to various embodiments there is provided a method forlithiation, or Li pre-doping, of an electrode. In some embodiments, themethod may include a Step 1 of preparing an electrode to be lithiated.The electrode may be a single electrode (i.e. a Stage 1 roll alsoreferred to as an electrode roll). Alternatively, the electrode may bepart of an electrode pack including wound or stacked electrode(s) andseparator(s), which may consist of at least one negative electrode, atleast one separator, and at least one positive electrode (i.e. a Stage 2electrode pack). Alternatively, the electrode may be part of anunfinished battery or ultracapacitor with an electrode pack includingwound or stacked electrode(s) and separator(s) inside a case and with orwithout an unsealed lid (i.e. a Stage 3 cell assembly). Step 1 mayinclude preparing the electrode roll, electrode pack, or cell assemblyin a normal air environment, drying it in a vacuum oven, and moving itinto a dry box or a small dry room. The method may further include aStep 2 of preparing a piece of Li metal with predetermined weightseparately in the dry box or the small dry room and, optionally,attaching the piece of Li metal to a conductive material with highconductivity, such as copper or nickel foil. The method may furtherinclude a Step 3 of attaching the piece of Li metal or the conductivematerial to a current collector of the electrode to be lithiated or to ametal tab connected to or from a current collector of the electrode tobe lithiated, a Step 4 of placing at least one such electrode roll,electrode pack, or cell assembly into a container, and a Step 5 offilling the container with electrolyte containing Li salts. The order ofthe steps can be changed. For example, Step 4 and Step 5 can bereversed. The Li metal may be located anywhere in relation to theelectrode. In some embodiments, the container inner wall may be madeconductive and the lithium metal can be attached on or be a part of theinner wall. In that case, Steps 3 and 4 can be reversed.

In the case of lithiation of the Stage 3 cell assembly, one of theoptions is that the cell packaging case containing the electrode packmay itself serve as the container of Steps 4 and 5, if the case is ametal or other conductive material. The most significant advantage ofthis approach is that the large dry room for the electrode preparationand the cell manufacture is not needed. Lithium is not introduced duringthe processes of preparing the electrode or electrode pack, e.g.jellyroll. It is introduced only during the later steps of the cellassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a view of a roll with a metal tab, apiece of lithium, electrolyte, and a container according to variousexample embodiments.

FIG. 2 is a diagram illustrating a roll with a metal tab attached to apiece of lithium.

FIG. 3 is a diagram illustrating a Stage 2 electrode pack consisting ofa positive electrode, a separator, and a negative electrode.

FIG. 4 is another diagram illustrating a Stage 2 electrode pack.

FIG. 5 shows an example operational flow of a lithiation method forproducing Li pre-doped electrodes.

DETAILED DESCRIPTION

While certain embodiments are described, these embodiments are presentedby way of example only, and are not intended to limit the scope ofprotection. The apparatuses, methods, and systems described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions, and changes in the form of the example methods andsystems described herein may be made without departing from the scope ofprotection.

Various embodiments provide a lithiation method for producing Lipre-doped electrodes. The lithiation method may reduce the manufacturetime and cost compared to the conventional Li attachment and pre-dopemethods, and may further prevent electrode and separator damage causedduring the pre-dope process in the direct contact methods. In somecases, it may reduce, minimize or eliminate the usage of a productionscale dry room. The lithiated electrodes may be incorporated into energystorage devices, for example, but not limited to, lithium-ion batteries,lithium-ion capacitors, etc.

FIG. 1 is a diagram illustrating a view of a roll 110 with a metal tab120, a piece of lithium 130, electrolyte 150, and a container 160according to various example embodiments. Referring to FIG. 1, at leastone metal tab 120 of the roll 110 may come from or be connected to acurrent collector 117 b (see FIG. 3) of the electrode to be lithiated.The roll 110 may consist of a single electrode (i.e. a Stage 1 roll alsoreferred to as an electrode roll) or a jellyroll consisting of at leastone negative electrode 116, one separator 114, and one positiveelectrode 112 as shown in FIGS. 3 and 4 (Stage 2 electrode pack for theexample of a cylindrical cell); or an unfinished battery orultracapacitor with an electrode pack inside and with a case and with orwithout an unsealed lid (Stage 3 cell assembly for the example of acylindrical cell).

A piece of Li metal 130 with predetermined weight, attached to aconductive material 140 with high conductivity, such as copper or nickelfoil, may be attached to the metal tab 120 or directly to the currentcollector 117 b (in which case the metal tab 120 may be omitted) of theroll 110. The roll 110 with optional metal tab 120 and the piece of Limetal 130 with conductive material 140 are placed inside a container 160filled with electrolytes 150 according to various embodiments. One roll110 with metal tab 120 may be connected to one or more pieces of Limetal 130 with conductive material(s) 140. Conversely, one piece of Limetal 130, optionally with conductive material 140, may be connected toone or more rolls 110 with metal tab(s) 120. Alternatively, the piece ofLi metal 130 with predetermined weight can be attached to the metal tab120 or current collector 117 b of the roll 110 directly, without beingattached to a conductive material 140. The metal tab 120 or currentcollector 117 b may be attached either to the piece of Li metal 130 or aconductive material 140 attached to the piece of Li metal 130. Thus, theelement labeled “130, 140” in FIGS. 2-4 may be either or both of thepiece of Li metal 130 and the conductive material 140.

The roll 110 and the piece of Li metal 130 may be connected to eachother through the metal tab 120 or directly through the currentcollector 117 b of the roll 110 (in which case the metal tab 120 may beomitted as noted above) and the optional conductive material 140attached to the piece of Li metal 130. The piece of Li metal 130 andoptional conductive material 140 can be located anywhere relative to theroll 110, within the bounds and flexibility of the metal tab 120 orcurrent collector 117 b. This includes the piece of Li metal 130 andoptional conductive material 140 being above, next to, or below the roll110. However, for a fast lithiation process, the piece of Li metal 130and optional conductive material 140 should be placed as close to theroll 110 as possible, preferably on the top or at the bottom of the roll110 (e.g. on a longitudinal axis L of a cylindrical jellyroll), as shownin FIGS. 2 and 3, where the lithiation paths 118 are along the surfacesof the negative electrode active layers 117 a. Therefore, the lithiationpaths 118 are along the surfaces of the negative electrode active layers117 a. As such, Li ions don't need to pass through the electrode 116,and a low cost solid metal foil can be used as the current collector 117b inside the electrode 116.

Another relative location of the piece of Li metal 130 and optionalconductive material 140 to the roll 110 is shown in FIG. 4, whichillustrates the Stage 2 roll 110 of FIG. 3, consisting of the positiveelectrode 112, separator 114, and negative electrode 116, along withanother separator 114. As in FIG. 3, the piece of Li metal 130 withpredetermined weight, attached to the conductive material 140 with highconductivity, such as copper or nickel, is attached to the metal tab 120or directly to the current collector 117 b (in which case the metal tab120 may be omitted) of the roll 110. However, in the example of FIG. 4,the piece of Li metal 130 with conductive material 140 is placed notabove or below the roll 110 but to the side of the roll 110 (e.g. offthe longitudinal axis L of FIG. 2). Therefore, the lithiation paths 118are perpendicular to the surfaces of the negative electrode activelayers 117 a, which may also be referred to as vertical to the roll 110.As such, Li ions need to pass through the electrode 116, and a high costmesh type metal foil or a high cost perforated metal foil must be usedas the current collector 117 b inside the electrode 116. Alternatively,if a solid metal foil is used inside the electrode 116 as the currentcollector 117 b, the electrode 116 may be perforated before making theStage 2 roll 110.

FIG. 5 shows an example operational flow of a lithiation method forproducing Li pre-doped electrodes. The operational flow may begin withpreparing the roll 110 in a normal air environment (step 510), dryingthe roll 110 in a vacuum oven (step 520), and moving the roll 110 into adry box or small dry room (step 530). The roll 110 may consist of asingle electrode such as the negative electrode 116 (Stage 1 roll alsoreferred to as an electrode roll). Alternatively, the roll 110 mayconsist of an electrode pack, e.g. a jellyroll, consisting of at leastone negative electrode 116, at least one separator 114, and at least onepositive electrode 112 (Stage 2 electrode pack for the example of acylindrical cell). Alternatively, the roll 110 may consist of anunfinished battery or ultracapacitor with an electrode pack, e.g. ajellyroll, inside a case and with or without an unsealed lid (Stage 3cell assembly for the example of a cylindrical cell). In any case, atleast one metal tab 120 may be connected to or from the negativeelectrode 116 to be lithiated (e.g. connected to or from a currentcollector 117 b thereof).

The operational flow may continue with preparing the piece of Li metal130 with predetermined weight separately in the dry box or the small dryroom (step 540) and, optionally, attaching the piece of Li metal 130 toa conductive material 140 with high conductivity, such as copper ornickel foil (Step 550), for example, by mechanical press. The piece ofLi metal 130 or, optionally, the conductive material 140 attachedthereto, may then be attached to the metal tab 120 or directly to thecurrent collector 117 b of the roll 110 (step 560), that is, the metaltab 120 or current collector 117 b of the negative electrode 116 to belithiated (or metal tab 120 or current collector 113 b of positiveelectrode 112 to be lithiated), for example, by welding (e.g. laserwelding, ultrasonic welding, cold welding). In this way, a single roll110, optionally with metal tab 120, may be connected to one or morepieces of lithium metal 130. Conversely, a single piece of lithium metal130 may be attached to one or more rolls 110 with metal tab(s) 120.

The operational flow may further include placing at least one roll 110and piece of Li metal 130 in the container 160 (step 570) and fillingthe container 160 with electrolyte 150 containing Li salts (step 580).The electrolyte 150 may be reusable during a process of lithiatingmultiple electrodes. The order of the steps is not limited to theexample shown in FIG. 5. For example, steps 570 and 580 can be reversed,with the container 160 first being filled with the electrolyte 150 andthereafter the roll(s) 110 and piece(s) of Li metal 130 being placed inthe container 160. The container 160 is a container for holding theelectrolyte 150. Lithiation or pre-doping may begin immediately afterthe roll(s) 110 and Li metal 130 (with optional conductive material) areconnected (via metal tab(s) 120 or directly via current collector(s) 117b) and placed inside the electrolyte 150 in the container 160.

The Li metal 130 may be located anywhere in relation to the roll 110 asdescribed above. In some embodiments, the inner wall of the container160 may be made conductive and serve as the conductive material 140 andthe piece of Li metal 130 can be installed on or be a part of the innerwall of the container 160. In that case, steps 560 and 570 can bereversed or occur substantially simultaneously, as the roll 110 isplaced inside the container 160 and attached to the inner wall thereof.

The container 160 of electrolyte 150 may contain one or more multiplerolls 110 with optional metal tab(s) 120 and may contain one or moremultiple pieces of Li metal 130 with optional conductive material(s)140. When the lithiation or pre-doping process is finished, the roll(s)with metal tab(s) 120 may be removed from the container 160.

In the case of lithiation of a Stage 3 cell assembly, one of the optionsis that the cell packaging case, i.e. the can in the example of acylindrical cell, outside of the electrode pack may itself serve as thecontainer 160. In this situation, the electrode pack, e.g. jellyroll,inside the can, may be regarded as the roll 110, and a piece of Li metal130 (and optional conductive material 140) may be connected to theelectrode pack and inserted into the can serving as the container 160.The can may then be filled with the electrolyte 150 to begin thelithiation or pre-doping process. In this case, excess Li metal 130 maybe removed from the can serving as the container 160 when the lithiationis complete. The most significant advantage of this approach is that thelarge dry room for the electrode preparation and the cell manufacture isnot needed. Lithium is not introduced during the electrode or electrodepack preparation process. It is introduced only during the late steps ofthe cell assembly.

This lithiation methods disclosed herein may need a longer lithiationtime than the direct contact method. However, the disclosed methods mayprevent the electrode, separator and cell damage caused by the shortingand strong reactions between the Li metal and the electrode beinglithiated. The method disclosed herein also provides lithiation pathsalong the electrode surfaces such that a low cost solid currentcollector can be used inside the electrodes.

Depending on whether a Stage 1, Stage 2, or Stage 3 roll 110 is to belithiated, the assembly of the electrodes or electrode packs (e.g.jellyrolls) or complete energy storage devices, such as battery andUltracapacitor, can be conducted in a normal air environment before theLi metal 130 is introduced and connected to the rolls 110. Thus, in thecase of a Stage 2 or Stage 3 roll 110, the dry room size requirementsmay be reduced. For Stage 3 roll lithiation, no dry room is necessary,since the lithium is introduced only at the last steps of cell assembly.After the electrodes, electrode packs (e.g. jellyrolls), or energystorage devices are prepared, the rolls 110 can be dried and moved intoa dry box or a small dry room and then connected to the piece of Limetal 130 and immersed in a container 160 filled with electrolytes 150containing Li salts. This eliminates the need for a full scale dry room,which can be very expensive to build, maintain, and operate.

In the above example embodiments of FIGS. 1-5, the disclosed methods aredescribed in relation to a cylindrical cell. However, the disclosedsubject matter is not intended to be so limited. As noted above, theinnovations describe herein apply equally in the case of non-cylindricalcells including, for example, pouch cells, button cells, or prismaticcells. Thus, throughout the description of FIGS. 1-5, the roll 110 maymore generally refer to an electrode roll, electrode pack, or cellassembly for any type of electrode cell, including, for example, a pouchcell in which the electrode pack comprises stacked rather than wouldelectrodes. Along the same lines, the container 160 is not limited to acan and may be, for example, a pouch of a pouch cell.

Although the present disclosure provides certain example embodiments andapplications, other embodiments that are apparent to those of ordinaryskill in the art, including embodiments which do not provide all of thefeatures and advantages set forth herein, are also within the scope ofthis disclosure. Accordingly, the scope of the present disclosure isintended to be defined only by reference to the appended claims.

What is claimed is:
 1. A method for lithiation of an electrode for usein an energy storage device, the method comprising: providing a cellassembly including a negative electrode, at least one separator, and apositive electrode, the negative electrode or the positive electrodebeing an electrode to be lithiated, the cell assembly being disposed inand electrically connected to a cell packaging case; providing a pieceof lithium metal with predetermined weight attached to a conductivematerial; attaching the conductive material with the piece of lithiummetal to an inner wall of the cell packaging case; and, after saidattaching the conductive material with the piece of lithium metal to theinner wall of the cell packaging case, and with the cell assembly beingdisposed in and electrically connected to the cell packaging case,filling the cell packaging case with an electrolyte containing a lithiumsalt.
 2. The method of claim 1, further comprising assembling the cellassembly without a dry box or dry room.
 3. The method of claim 1,wherein the cell assembly includes a plurality of negative electrodes, aplurality of separators, and a plurality of positive electrodes.
 4. Themethod of claim 1, wherein said attaching includes positioning theconductive material above or below the cell assembly.
 5. The method ofclaim 4, wherein said attaching includes positioning the conductivematerial on a longitudinal axis of the cell assembly.
 6. The method ofclaim 1, wherein the electrode to be lithiated includes a currentcollector formed from a solid metal foil.
 7. The method of claim 1,further comprising, after lithiation of the electrode to be lithiated,removing the conductive material and the remains of the piece of lithiummetal on the conductive material from the cell packaging case.
 8. Amethod for lithiation of an electrode for use in an energy storagedevice, the method comprising: providing a cell assembly including anegative electrode, at least one separator, and a positive electrode,the negative electrode or the positive electrode being an electrode tobe lithiated, the cell assembly being disposed in a cell packaging case;providing a piece of lithium metal with predetermined weight; attachingthe piece of lithium metal to a current collector of the electrode to belithiated or to a metal tab connected to or from a current collector ofthe electrode to be lithiated; and, after said attaching, and with thecell assembly being disposed in the cell packaging case, filling thecell packaging case with an electrolyte containing a lithium salt. 9.The method of claim 8, further comprising assembling the cell assemblywithout a dry box or dry room.
 10. The method of claim 8, wherein thecell assembly includes a plurality of negative electrodes, a pluralityof separators, and a plurality of positive electrodes.
 11. The method ofclaim 8, further comprising positioning the piece of lithium metal aboveor below the cell assembly.
 12. The method of claim 11, furthercomprising positioning the piece of lithium metal on a longitudinal axisof the cell assembly.
 13. The method of claim 8, wherein the currentcollector is formed from a solid metal foil.
 14. The method of claim 8,wherein the attaching includes attaching the piece of lithium metal tothe current collector or to the metal tab via a conductive path thatdoes not include the cell packaging case.
 15. The method of claim 8,further comprising, after lithiation of the electrode to be lithiated,removing the remains of the piece of lithium metal from the cellpackaging case.
 16. A method for lithiation of an electrode for use inan energy storage device, the method comprising: providing a cellassembly including a negative electrode, at least one separator, and apositive electrode, the negative electrode or the positive electrodebeing an electrode to be lithiated, the cell assembly being disposed inand electrically connected to a cell packaging case; providing a pieceof lithium metal with predetermined weight; attaching the piece oflithium metal to an inner wall of the cell packaging case; and, aftersaid attaching the piece of lithium metal to the inner wall of the cellpackaging case, and with the cell assembly being disposed in andelectrically connected to the cell packaging case, filling the cellpackaging case with an electrolyte containing a lithium salt.
 17. Themethod of claim 16, further comprising assembling the cell assemblywithout a dry box or dry room.
 18. The method of claim 16, wherein thecell assembly includes a plurality of negative electrodes, a pluralityof separators, and a plurality of positive electrodes.
 19. The method ofclaim 16, wherein said attaching includes positioning the piece oflithium metal above or below the cell assembly.
 20. The method of claim19, wherein said attaching includes positioning the piece of lithiummetal on a longitudinal axis of the cell assembly.